Secondary Alloy Research Articles

Effect of annealing treatment on microstructure and tensile properties of Ti-48Al-2Cr-5Nb alloy fabricated by laser additive manufacturing

Using laser additive manufacturing (LAM), a Ti-48Al-2Cr-5Nb alloy was fabricated and studied systematically for its microstructure, phase composition, texture, and tensile properties. The results indicate that both the microstructure of as-deposited and annealed alloys consists of phases Ti3Al (α2) and TiAl (γ). When the annealing temperature was increased, the microstructure changed significantly and a greater amount of lamellar α2 phase precipitated between the lamellae. Meanwhile, the thickness of γ lamellar at the edges of lamellar clusters increased. In comparison with the annealed alloy, the secondary annealed alloy demonstrated a significant coarsening of the lamellar γ phase. Increasing the annealing temperature gradually increased the texture strength of the γ (111) orientation. At room temperature and high temperature, the as-deposited alloy had a higher tensile strength than the annealed alloy. Ti-48Al-2Cr-5Nb alloy samples secondary annealed at 1260 °C/1h/FC exhibited the highest elongations at room temperature, 750 °C, and 850 °C, with values of 1.6%, 3.8%, and 4.8%, respectively. As compared to the as-deposited alloy, the elongation increased by 1.15, 1.36, and 1.07 times, respectively.

Small-angle neutron scattering applied to low-dose neutron-irradiated Fe-Cr alloys and ferritic martensitic steel Eurofer97.

Ferritic/martensitic (F/M) Fe-Cr-based steels are candidates for applications in nuclear fission and fusion. Previous experimental results for neutron-irradiated binary Fe-Cr alloys and high-dose neutron-irradiated F/M steels contributed greatly to the understanding of the irradiation behaviour of these groups of materials. However, some details still need to be addressed. Such gaps are related to the effect of secondary alloying and impurity elements, such as Ni and Si, as well as the dose dependence at lower neutron doses [e.g. in the range 0.1-1 displacements per atom (dpa)]. This input is essential, for example, for multiscale modelling of irradiation effects or the evaluation of nuclear fission or fusion components at the first stages of operation. Using small-angle neutron scattering, three issues are addressed: (1) the effect of Cr undersaturation (5% Cr) and supersaturation (14% Cr) on the formation of irradiation-induced solute atom clusters/precipitates in low-dose neutron-irradiated Fe-Cr alloys in the presence of intentionally added levels of Ni, Si and P; (2) the effect of irradiation temperature (290°C versus 450°C); and (3) the effect of neutron dose in the range 0.06-0.6 dpa on the irradiation response of the reduced-activation F/M 9%Cr steel Eurofer97. The irradiation-enhanced formation of Cr-rich α'-phase particles was found to be the dominant effect for supersaturated Fe-14Cr-NiSiP at both irradiation temperatures. In contrast, α' formation is impossible in Fe-5Cr-NiSiP, for which the pronounced irradiation effects observed at 0.1 dpa are mainly attributed to added Ni, Si and P. Finally, Eurofer97 exhibits an exceptionally weak irradiation effect at low neutron doses, the reasons for which are also considered.

Quality of automotive sand casting with different wall thickness from progressive secondary alloy

Abstract This paperwork is focused on the quality of AlSi6Cu4 casting with different wall thicknesses cast into the metal mold. Investigated are structural changes (the morphology, size, and distribution of structural components). The quantitative analysis is used to numerically evaluate the size and area fraction of structural parameters (α-phase, eutectic Si, intermetallic phases) between delivered experimental material and cast with different wall thicknesses. Additionally, the Brinell hardness is performed to obtain the mechanical property benefits of the thin-walled alloys. This research leads to the conclusion, that the AlSi6Cu4 alloy from metal mold has finer structural components, especially in small wall thicknesses, and thus has better mechanical properties (Brinell hardness). These secondary Al-castings have a high potential for use in the automotive industry, due to the thin thicknesses and thus lightweight of the construction.

Influence of modification with highly dispersed silicon carbide on the casting properties of the secondary alloy of the Al-Si system

One of the main areas of application of aluminum is the aerospace and transport industries, which are constantly increasing the requirements for the properties of cast products. The use of aluminum as the main material for the manufacture of various parts of vehicles can significantly reduce their weight, which leads to a decrease in fuel consumption. In order to meet the requirements of the modern world, the work considers studies to improve the quality and increase the properties of products from the secondary aluminum alloy AlSi12. Modern technologies for processing liquid aluminum alloy are analyzed. According to the results of an analytical review, it was found that modifiers that affect the size of the primary grain and the shape of inclusions of eutectic silicon are of the greatest interest. It was found that the modification processes do not change the chemical composition of the alloy, but rather contribute to a change in the size and shape of the structural components of the alloy. The paper considers the influence of an ultradispersed SiC modifier with a particle size of up to 200 nm on the casting properties of secondary aluminum alloys: fluidity, linear and volumetric shrinkage. The fluidity was studied in green sand and metal mould. It was found that the addition of 0.1 % SiC improves the fluidity of the secondary alloy from 560 to 630 mm for green sand mould and from 230 to 295 mm for a metal mould due to cleaning from non-metallic inclusions. A further increase in the SiC content to 0.2 % does not lead to an obvious increase in fluidity. The study of linear shrinkage found that increasing the content of the modifier to 0.2 % contributes to its decrease. At the same time, an increase in the pouring temperature of the alloy promotes an increase in the total linear shrinkage, which is associated with the long residence time of the metal in the liquid state. As a result of the rapid crystallization of the melt with additional nucleation centers in the role of which are particles of the ultradispersed modifier, the coefficient of volumetric shrinkage decreases from 28 to 20 %. The proposed technical solutions for the modification of alloys of the secondary alloy AlSi12 can be used in processes that will improve the quality of cast metal products with the economical use of energy resources and materials for its production.

Effect of different chloride environments on corrosion behavior of secondary AlSi7Mg0.6 cast alloy with higher Fe content

Secondary aluminum alloys are materials with higher Fe content. There are currently several studies on the corrosion behavior of casts from metal molds, but sand casts are being forgotten despite being still primarily used in gravity casting. Secondary Al-alloys have exceptional benefits as they are made from scrap and can be cast as thin-walled, which has a positive effect on the lightening of constructions, and on environmental impact. Unfortunately, the Fe is a common impurity but in higher content decrease properties of aluminum casts. The removal of the Fe content is very expensive, and therefore the effect of Fe content in a larger amount is monitored. This work is focused on the corrosion behavior of the heat-hardening aluminum alloys commonly used to produce castings AlSi7Mg0.6 for automotive. The experimental alloy was intentionally contaminated with Fe for reaching the critical amount of Fe in aluminum casts. Metallographic analysis (using optical and scanning electron microscopy, energy dispersive X-ray analysis) was used before corrosion tests. The microstructure of experimental alloys with higher content of Fe contains large Fe-rich phases in the form of needles. These changes in microstructure lead to the formation of a higher amount and size of porosity but the α-phase was not affected. Corrosion properties were examined by three basic corrosion tests: immersion test, potentiodynamic test, and Audi test. Corrosion characteristics of materials were evaluated using a stereo and optical microscope. Corrosion evaluation of the alloys shows the presence of pitting corrosion, which increases with increasing Fe content.

Forecasting global aluminium flows to demonstrate the need for improved sorting and recycling methods.

The probable emergence of a global aluminium scrap surplus in the coming decade is one of the main incentives for the aluminium recycling industry to invest in new methods and technologies to collect, sort and recycle aluminium scrap. However, due to the considerable uncertainty in the evolution of the global scrap surplus, it is difficult for policymakers and the recycling industry to accurately estimate the economic and environmental advantages of implementing enhanced sorting and recycling methods. The International Aluminium Institute (IAI) has developed a model to track and forecast the global flows of aluminium, but this model is not extensive enough to estimate the scrap surplus evolution. Therefore, this paper introduces an alloy series resolution to the supply and demand of aluminium in the IAI's global flow model and estimates the composition of the recovered scrap flows to improve the estimate of the technical potential of secondary alloy production. The estimated scrap surplus evolution is subjected to a sensitivity analysis, considering the most critical parameters, including the speed of electrification in the automotive sector, the recovered scrap's composition and the lifetime of aluminium products. In addition, the estimated composition of the recovered aluminium scrap in the model is compared to composition measurements of alumimium scrap collected at a Belgian recycling facility as a means of validation. This study allows to estimate that the global aluminium scrap surplus will emerge soon and reach a size of 5.4 million tonnes by 2030 and 8.7 million tonnes by 2040, if currently adopted aluminium sorting and recycling methods are not improved.

Effect of bifilm defects on Microstructure and Tensile properties of A356 secondary alloy for the recycling of machining chip scrap

Effect of bifilm defects on Microstructure and Tensile properties of A356 secondary alloy for the recycling of machining chip scrap

Effect of nickel on the high-pressure phases in FeH

Hydrogen-rich metal alloys and compounds have drawn interest from planetary geophysics and condensed matter physics communities because of their potential for deep hydrogen storage in planets and high-temperature superconductivity. We find that a small amount of Ni can alter the phase behavior in the FeH alloy system. Ni can stabilize the double hexagonal close-packed (dhcp) structure in FeH up to the liquidus at 33 GPa, which is in contrast with the stability of the face-centered cubic (fcc) structure in Ni-free FeH at the same conditions. Above 60 GPa, Ni suppresses the stability of the tetragonal ${\mathrm{FeH}}_{2}$ phase but stabilizes fcc FeH at higher temperatures. At the same pressure range, we find tetragonal ${\mathrm{FeH}}_{2}$ and cubic ${\mathrm{FeH}}_{3}$ to be stable at temperatures above 2500 K without Ni. Therefore, in planetary interiors, Ni will expand the stability field of dense close-packed structures in the FeH system. If the Ni content is low, then ${\mathrm{FeH}}_{2}$ and ${\mathrm{FeH}}_{3}$ can play an important role in the cores of hydrogen-rich planets. Also, our study demonstrates that a secondary alloying component can severely impact the high-pressure stability of polyhydrides.

Investigation of mechanical properties of secondary AlSi7Mg0.3 cast alloys before and after corrosion

The casting industry currently use about 35% of secondary (recycled) aluminum and about 65% of primary aluminum to meet their needs. The manufacturer wants to use the secondary aluminum alloys more and more, but these materials have the higher amount of the undesirable elements. The most negative element in such alloys is Fe. Although the corrosion current increased due to the presence of alloying elements in the matrix of aluminum alloys, the higher content of Fe (which led to increasing amount of Fe-rich phases) could affect the corrosion resistance. The basic metallography assessment of experimental materials microstructure confirm the higher amount of Fe-rich phases in secondary alloys. The results of mechanical properties shows that the higher content of Fe (also Fe-rich phases) does not lead to decreasing the mechanical properties. The similar results of mechanical properties were reached after corrosion attack with 3.5 wt. % NaCl. The assessment of corrosion attack confirmed the presence of pitting corrosion on experimental samples, which increase with increasing Fe content.

Comparative Study of the Metallurgical Quality of Primary and Secondary AlSi10MnMg Aluminium Alloys

The use of secondary aluminium is increasingly being promoted in the automotive industry for environmental reasons. The purpose of this study was to demonstrate that it is possible to obtain a recycled AlSi10MnMg(Fe) aluminium alloy with equal metallurgical quality to that of a primary AlSi10MnMg alloy when an adequate melt treatment is applied. The melt treatment consisted of deoxidation, degassing and skimming in accordance with the detailed procedure described in this article. The metallurgical qualities of one primary and two secondary alloys were assessed using thermal analysis, the density index test, the macroinclusion test and the microinclusion level test before and after melt treatment. The thermal analysis allowed us to compare the variables of the solidification cooling curve (Al primary temperature and its undercooling; Al-Si eutectic temperature and its predictive modification rate). The density index test was used to evaluate the hydrogen gas content in the melt. The macroinclusion test was used to evaluate the melt cleanliness, while the microinclusion level test was used to perform the inclusion identification and quantification analyses. This study showed the feasibility of manufacturing structural components using 100% recycled secondary aluminium alloy through V-HPDC technology.

PROSPECTS FOR IMPROVING THE PROPERTIES OF SECONDARY FOUNDRY ALLOYS OF THE AL-SI SYSTEM USING THE MODIFICATION PROCESS

The results of analytical studies of the use of modern modifiers for secondary aluminum alloys, which affect the structure of the metal of castings and allow to obtain the necessary physical and mechanical characteristics. It is shown that modifiers influencing the size of the primary grain and the shape of eutectic silicon inclusions are of the greatest interest for the production of castings from secondary silumins. It is shown that according to modern ideas the structure of the metal melt is not homogeneous. In some temperature range, complete mixing of atoms does not occur, and microregions with a short-range structure characteristic of the crystalline phase appear. These formations are called differently: atomic groups, clusters, clots, islands, complexes of atoms, clusters, etc. In the last decade, ultrafine powders of chemical compounds (nanopowders), which act as additional crystallization centers during primary crystallization, have become increasingly used as modifiers of cast alloys.

Study of monotonic and cyclic mechanical behavior and microstructural evolution at a high temperature of ASTM A297 HP steel modified with niobium

The present work studies the effects of niobium on the mechanical properties and the elastoplastic/viscoelastic behavior at 927 °C of ASTM A297 grade, HP cast stainless steel in the as-cast material, to simulate the actual work condition. Tensile tests were carried out at different temperatures, differential scanning calorimetry (DSC), relaxation tests, the fatigue of continuous cycles under the triangular waveform, and fatigue with a trapezoidal waveform of the type “Dwell” with dwell times of 120 and 300 s as specified in the E2714-13 standard and hot torsion tests, to analyze the variations in the mechanical properties. The results of the mechanical tests and studies of the microstructural evolution, as well as of its later analyzes, provided data, not only in the form of data sheet's for the application of the values obtained in projects but concurrently after comparing property and microstructure, to deepen the phenomenology of mechanical stress behavior versus monotonic and cyclic deformation, high-temperature deformation mechanisms, dynamic recovery, of the type of microstructure resulting after the tests and also of the fracture mechanisms associated with the types of mechanical stresses imposed on the material, obtained by through the mechanical tests mentioned above. The high-temperature fatigue tests showed expected stress versus strain behavior, where cycles without dwell times showed lower hysteresis area values, from where the energy consumed in a strain cycle is calculated. The increase in the consumed energy values is due to the insertion of the dwell times, but it is important to note that for the tests that contain dwell times of 120 s and 300 s they did not show significant differences between the consumed energy, showing a saturation effect of tension that does not promote more significant inelastic strains. The cyclic mechanical fatigue stresses with dwell times and the low deformation rate led to intense precipitation of secondary carbides Cr23C6 chromium alloys added to the intrinsic properties of stainless steel dislocation slip were factors that resulted in the dynamic recovery phenomenon. Fractographic analyzes performed on monotonically fractured specimens and specimens after fatigue tests revealed that the material is prone to fracture in intergranular regions.

Analysis of hydrogen behavior by crystallization of secondary aluminum alloy

Methodology. There was conducted the process modeling of hydrogen by crystallization of secondary aluminum alloy. Findings. There was conducted an analysis of hydrogen behavior by indurating secondary aluminum alloy castings. There were obtained expressions for calculation of the current value in the process of secondary aluminum alloy crystallization of the hydrogen density in the boundary diffused layer, on the crystallization front, in the volume of the remaining melt, and the effective hydrogen distribution coefficient. Originality. For the first time, there was obtained an arithmetic model for the forecasting of hydrogen behavior by indurating secondary aluminum alloy castings. Practical value. The results of the study can be implemented with the purpose of the flow optimization process and the more efficient use of expensive equipment for getting high-quality secondary aluminum alloy castings. Keywords: aluminum, secondary aluminum alloys, indurating, hydrogen, crystallization front, distribution coefficient, boundary diffusion layer.

Characterization of Aluminum Alloy–Silicon Carbide Functionally Graded Materials Developed by Centrifugal Casting Process

The continuous development of modern industries rises the necessity for functionally graded materials. This research starts from the consideration that the incorporation of SiC particles in the molten aluminum alloy can be difficult due to the very low wettability of SiC particles. In order to increase their wettability, SiC particles were covered with a layer of metallic copper. The incorporation of SiC particles into the aluminum alloy mass was performed by centrifugal casting. The secondary hypoeutectic Al-Si alloy used in this study was elaborated within the crucible of a resistors heated furnace. The metallic coating of SiC particles, in addition to the effect of increasing their wettability by molten metal, also has a role in preventing the formation of aluminum carbide in case of heating above 700 °C. A great amount of attention was paid to the parameters used during the centrifugal casting process. The results showed that adjusting the proportion of SiC particles within the composite allows us to obtain values of the thermal expansion coefficient within previously established limits. The present work demonstrates that the coating of SiC particles covered with a thin layer of metallic Cu creates the conditions to easily incorporate them into the molten Al mass, thus obtaining FGMs with controlled properties.

Possibilities of predicting undesirable iron intermetallic phases in secondary Al-alloys

Today, aluminium is becoming the preferred construction material for transportation applications because it combines three basic properties: strength, durability and lightness. The use of aluminium castings is increasing in a wide range of transport applications. Another advantage of using aluminium materials is their ability to recycle. The use of recycled secondary aluminium alloy has many advantages; it is not only environmentally but also cost-effective. However, the main disadvantage of using a secondary aluminium alloy is the higher amount of iron. Iron in aluminium alloys forms various types of Fe-rich intermetallic phases. It is necessary to control the amount of iron and prediction the formation of undesirable iron intermetallic phases as "sludge" phases, and β-phases. β-phases cause feeding problems, create places with increased concentration of stress, increase casting porosity, and generally reduce plastic properties of the cast alloys. Sludge phases can compromise the machining operations, with a considerable effect on the cutting tool life, and even more degrade the mechanical and physical properties of the component. For the study and identification of intermetallic phases were used equations for calculating SF and critical iron content and observation on the microscope. The results show that coarse sludge, Fe-rich phases appear in the alloy D with 1.200 wt. % Fe. The value critical amount of iron has exceeded in alloy B with 0.679 wt. % Fe, alloy C with 1.209 wt. % Fe, and alloy D with 1.200 wt. % Fe.

Influence of iron content on SDAS factor, Al5FeSi intermetallic phases and porosity of the secondary aluminum alloy AlSi7Mg0.6 used in the automotive industry

This paper is focused on evaluating the influence of iron content on SDAS factor, Al5FeSi phase size, and porosity of secondary aluminum alloy AlSi7Mg0.6 used in the automotive industry. These characteristics were evaluated by quantitative analysis on sand-casted experimental alloys with various iron contents (0.128; 0.202; 0.429; 0.75; 1.264 %). Results have shown a decrease of SDAS factor with increasing of iron content. Al5FeSi phase average length and thickness values increased with the rising iron content. These dependencies began to reveal themselves when the iron content reached values around the critical value of the iron content - Fecrit. (0.475 % Fe). The average area of pores (2.05 - 3.8 %) and pore size (39 597 - 70 332 µm2) increased with increasing of iron content (0.128; 0.75; 1.264 %) too.

Metal-based systems allowing the use of scrap to prepare aluminum alloys

The amount of scrapped structures and components made of aluminum alloys is constantly growing along with the increase in the demand for the use of aluminum alloys in various industrial sectors. Uzbekistan has been showing a trend of developing industrial production at a pace typically observed in highly developed countries. In Uzbekistan, the aluminum alloys are used for widespread applications in construction, engineering, energy, chemistry and chemical technology, etc. Due to lack of primary aluminium production facilities in the country, there is a need for the collection and deep processing of the scrapped parts that have fulfilled their useful life. This practice is well implemented and working well for the collection of parts from Al – Si based alloys, also called silumins. The composition, structure and properties of many secondary silumins, which have found application in mechanical engineering, have been developed and improved. For alloys of the Al – Si system, most of research activities focused on property improvement through microalloying as well as improvements in the casting technology and heat treatments. However, it is too early to talk about a systematic approach to improving the operational properties of silumins. This also fully applies to alloys of other systems based on aluminum, for example, Al – Mg alloys, also called magnalias. For Uzbekistan, this is very important, since, as analysis shows, the aluminum alloys of 6XXX family are predominantly used for the construction and building structures. After the development of the first secondary wrought alloy of aluminum with the main alloying element with magnesium, many works were published with the results on improving the composition, structure, properties, processing technologies of secondary magnesia. The published works are notable for the inconsistency of the authors’ positions on microalloying systems and the thermal treatment of secondary magnalias. Regarding silumins, all the results are experimental, there is no systematic approach to the development of new and improvement of the properties of existing alloys from scrapped parts. Based on the experimental results, the article proposes an attempt of a systematic approach to the choice of alloy composition, microalloying systems, optimization of the composition of aluminum alloys for industry.

Increasing secondary silumins quality in the condi-tions of prezent day production

Due to the lack of domestic production of primary aluminum in Ukraine, an actual problem is the development of technological processes for producing high-quality aluminum alloys using secondary raw materials. It is known that secondary aluminum raw materials are characterized by a high content of undesirable impurities, which makes it difficult to obtain alloys with the required level of technological and mechanical properties. Goal. The aim is development of a technology for the production of aluminum alloys from secondary raw materials that meet the requirements of modern standards and technical conditions. Methodology. Development of a complex technology, including the hereditary modification of liquid metal by a fine crystalline charge and impurity modification by modifier MK-1. Results. Complex modification provided a reduction in the size and shape parameter of intermetallic phases and silicon particles, which positively affected the mechanical properties of the alloys. Originality. It was established that complex modification made it possible to neutralize the negative effect of iron, which is the most harmful impurity in secondary alloys. It was established, that silumin AK7 with Fe content up to 1.84 % meets the requirements of the standard for mechanical properties. Practical value. The results of industrial tests showed that the developed technology of complex modification expands the possibilities of producing silumins of the required quality using cheap secondary raw materials.

Analysis of the Mechanical Properties of Secondary AlZnMg(Cu) Die-Cast Alloys

In this work, the development of AlZnMg(Cu) alloys was performed by thermodynamic simulations and experimental tests. With calculations, the solidification processes and phase compositions could be predicted. As secondary casting alloys, the selected compositions of AlZn4Mg3Cu(Fe) and AlZn5Mg4Cu have higher contents of alloying elements, such as iron and silicon, and were successfully processed with a cold-chamber die casting machine. In addition, an energy- and time-saving optimization of the material properties was performed by a modified heat treatment (T6*) with a total time of only 12 h. The alloys were evaluated based on the characterization of their mechanical properties and the analysis of their microstructures. In particular, the elimination of cost-intensive alloying elements and the application of a modified heat treatment method clearly show the potential of AlZnMg(Cu) die-cast alloys for future industrial use.

The Failure Degradation of Recycled Aluminium Alloys with High Content of β-Al<sub>5</sub>FeSi Intermetallic Phases

In this study, the effect of the β-Al5FeSi phases on fracture surfaces in secondary AlSi7Mg0.3 cast alloys with common and higher amount of iron was investigated. Iron addition caused the formation of different Fe-rich intermetallic phases in aluminium alloys. Components made of secondary aluminium alloys commonly have a higher amount of such phases. Sharp needles as β-Al5FeSi phase lead to initiate stress tension, thereby contributing to increased risk of micro-cracks formation on the fracture surfaces. To determine the effect of β-Al5FeSi to fracture surfaces of AlSi7Mg0.3 cast alloy, SEM microscopy with energy-dispersive X-ray spectroscopy (EDX) was used to study the amount of needles phases, their morphology and violation wave. It was found that increasing Fe content increased the size and the number of Al5FeSi phases. The fractographic analysis of fracture surfaces shows an increasing amount of cleavage fracture in materials with a higher amount of iron, too.